BEIRUT: Syrian elite troops advanced on the key rebel-held neighborhood of Baba Amr in Homs Wednesday, with a Syrian official vowing it would be “cleansed,” raising fears of a ground operation to retake all of the central city.

“Pray for the Free Syrian Army. Do not be miserly in your prayers for them,” opponents of President Bashar Assad said in a statement, as diplomats spoke of his brother’s feared 4th Armored Division mounting a drive to “finish off” the rebels.

The motley band of army deserters and desperate insurgents who call themselves the Farouq Brigade of the Free Syrian Army have sworn to fight to the last man, one activist from Baba Amr told Reuters. Others, though, said some of the unit’s leaders had already made their escape from the shattered area.

The 4th Armored Division commanded by Maher Assad, the president’s younger brother, has a reputation for ruthlessness burnished during the past year of revolt and forged in history after the role its predecessor units played in massacring many thousands of Sunni Islamists at Hama in 1982 on the orders of Assad’s father Hafez.

Details from Homs were sketchy, with communications channels to the city blacked out.

Syria refused to allow a visit to the country by a senior U.N. humanitarian envoy, Valerie Amos, as a senior Western diplomat told Reuters: “All the signs out of Homs are that they’re trying to finish it off.

“They clearly feel that letting her in now would be devastating for their image – as indeed it would be.”

A security source told AFP in Damascus that Baba Amr was “under control,” after activists reported troops from then 4th Armored Division had taken up positions around the neighborhood.

“The army has started combing the area building by building and house by house. Now the troops are searching every basement and tunnel for arms and terrorists,” the security source said. “There remain only few pockets” of resistance.

But while Homs-based activist Hadi Abdullah reported clashes and heavy shelling of Baba Amr, he insisted ground troops had not yet entered.

“Regime forces did not enter Baba Amr until this moment. They are surrounding the district, while clashes are concentrated in the neighborhoods of Inshaat and Malaab,” he said.

Abdullah said activists were “evacuating families because shelling has been targeting places that were considered safe in the past.”

As news of the assault trickled through, the United States summoned Syria’s envoy in Washington to express “outrage” over his government’s month-long bombardment.

During talks at the State Department with Syrian Charge d’Affaires Zuheir Jabbour, U.S. Assistant Secretary of State Jeffrey Feltman also urged Syria to live up to its Nov. 2 commitment to the Arab League to end such violence.

The meeting was “to express our outrage over the month-long campaign of brutality and indiscriminate shelling of the city of Homs,” the State Department said in a statement.

In a high risk, three-day operation, Spanish reporter Javier Espinosa, one of four Western journalists trapped in Baba Amr for a week, crossed into Lebanon Wednesday, activists said, following the rescue Tuesday of wounded British photographer Paul Conroy. Human Rights activists Avaaz, who have played a key role in the evacuation, said 13 “unarmed humanitarian activists” had been killed in the operation in which 47 wounded Syrians had also been safely retrieved.

Espinosa left Baba Amr with Conroy Sunday night but was separated from the rescue convoy along with French journalists William Daniels and Edith Bouvier when the group came under a shelling attack by Syrian forces, Avaaz said.

It is understood Bouvier and Daniels returned to Baba Amr, and Avaaz said they had had no contact with the pair since Sunday night.

Bouvier was wounded in a Feb. 22 bombardment which killed veteran Sunday Times war correspondent Marie Colvin and French photographer Remi Ochlik. Their bodies remain in Baba Amr.

In a conflicting account, activists network the Local Coordination Committees said Bouvier was refusing to leave Baba Amr without the presence of the French ambassador and in solidarity with other injured Syrians.

YouTube footage posted by activists showed army trucks and tank carriers on a highway, purportedly heading for Homs. Images and reports of events could not be verified by The Daily Star.

A spokesman for the International Committee of the Red Cross, Hicham Hassan, said the violence in Homs was making the humanitarian situation more difficult. “This makes it even more important for us to repeat our call for a halt in the fighting,” he told Reuters in Geneva.

Activists say hundreds of civilians have been killed in besieged opposition districts of Homs, including at least 20 Tuesday. Shells and rockets have been crashing into Baba Amr since Feb. 4. Army snipers are purportedly shooting at civilians who venture out.

The ICRC said its Syrian Red Crescent affiliate had established 10 distribution and first aid points in Homs, but had been unable to operate in Baba Amr because of the violence.

Troops also bombarded the besieged town of Rastan, 20 km north of Homs, and several people were killed when a shell hit a house, the Syrian Observatory for Human Rights said.

Activists said troops and pro-Assad militiamen had also attacked the town of Helfaya, an opposition stronghold near Hama, detaining people and raiding and burning houses.

The United Nations says Assad’s security forces have killed more than 7,500 civilians since the revolt began last March. Syria’s government said in December that “armed terrorists” had killed more than 2,000 soldiers and police during the unrest.

United Nations humanitarian chief Amos said she was “deeply disappointed” Syria refused to let her visit the country, while the senior Western diplomat who spoke of efforts to “finish off” the rebels in Homs said Syria had decided to deny Amos entry “despite Russian efforts to get her access.”